Production of benzene hexachloride



Patented Oct. 26, 1954 PRODUCTION OF BENZENE HEXACHLORIDE William E.Bissinger, Akron, Ohio, assignor, by

mesne assignments, to

Columbia-Southern Chemical Corporation, Pittsburgh, Pa., a corporationof Delaware No Drawing. Application February 8, 1950, Serial No. 143,147

7 Claims. 1

This invention relates to the preparation of benzene hexachloride, andit has particular relation to the preparation of benzene hexachlorideunder conditions which will not darken the benzene hexachloride therebyproduced.

It is known that benzene hexachloride may be prepared by reaction ofbenzene with chlorine in the absence of a chlorination substitutioncatalyst, such as ferric or aluminum chloride. This reaction may befacilitated by actinic light and/or by employing organic peroxides as acatalyst, such as described in a co-pending application, Serial No.15,487, filed March 17, 1948, of William E. Bissinger and FranklinStrain, and now abandoned. Actinie light may be defined as light, thewave length of which is from 2500 to '4500 Angstrom units, or at leastabove the visible range, in frequency. It may also be defined as lightwhich produces chemical change.

Several methods of preparing benzene hexachloride may be used. Accordingto one such method, chlorine gas is reacted with an excess of benzene ator near room temperature, while irradiating the mixture with actiniclight. According to a further method, benzene and liquid chlorine may bereacted at a temperature and pressure such as to maintain the chlorinein the liquid state. Temperatures which have been used in the lattermethod have usually been from C. to minus 33.7 C. Actinic light isgenerally used to promote the reaction, although the reaction usingliquid chlorine is reported to proceed even in the dark.

At least five isomeric forms of benzene hexachloride are produced byconventional addition chlorination processes. These isomers have beendesignated as alpha, beta, gamma, delta, and epsilon isomers. Forcertain purposes, such as in the insecticidal field, it isconventionally recognized that a high content of the gamma isomer isdesirable.

In the methods set forth above for producing benzene hexachloride, andin most methods of producing benzene hexachloride by reacting chlorinewith benzene, it is necessary to separate the product, benzenehexachloride, from the reaction mixture. Usually present, with the solidbenzene hexachloride product, are benzene, and chlorinated benzenes,such as monochlorobenzene and dichlorobenzene. One objectionable featureof the presence of these compounds is that they render the product muchmore difficult to grind to a pulverulent particle size. These compoundslower the melting point of the product and this causes plugging in thegrinder.

These agents or impurities may be removed from the benzene hexachlorideby heating the reaction mixture or by heating crude benzene hexachlorideafter separation from the reaction mixture.

One undesirable feature, however, of this method of recovering benzenehexachloride in a substantially pure state, is that the product tends todiscolor when the reaction mixture of the crude benzene hexachloride isheated. When liquid chlorine is employed in the production of benzenehexachloride the discoloring often appears at temperatures even as lowas 50 C. and in other processes the color of the product usually willhave begun to turn black after a temperature of about 100 C. has beenreached. Such discoloration is highly undesirable, and is believed to bedue to the presence of certain impurities, possibly metallic compounds.

In accordance with the present invention, a nove1 process for preparingbenzene hexachloride as a white, highly pure, pulverulent product hasbeen discovered. It has been found that the impurities may be removedfrom benzene hexachloride by heating benzene hexachloride in' thepresence of a phosphorus compound of the type hereinafter set forth.Most effective results are obtained by reacting chlorine in theelemental state with benzene, in the presence of the phosphorus compoundand thereafter subjecting the resulting benzene hexachloride to theabove purification process. This reaction may be conducted convenientlyby bubbling gaseous chlorine through liquid benzene containing suchphosphorus compound, at a convenience temperature, usually below C., forexample room temperature or below, or by reacting benzene with liquidchlorine or by other method. It is desirable that the phosphoruscompound be present during part, and preferably all, of the chlorinationreaction in order to prevent discoloration during the purification step;however color improvement may also be attained by adding the phosphoruscompound after chlorination but before heating of the reaction slurry.It is essential in order that such undesirable color formation beprevented, that the reaction mixture or slurrry containing thephosphorus compound be thoroughly agitated.

The following compounds of phosphorus are contemplated in the inventionas being useful in the prevention of 'discoloring of benzenehexachloride during purification by heating:

Phosphoryl chloride, phosphorus pentachloride, and phosphorus oxides,such as phosphorus trioxide, phosphorus tetraoxide and phosphoruspentoxide, prevent darkening, as well as do the hydrates of thesephosphorus oxides, such as phosphorous acid and ortho-, meta-, andpyrophosphoric acid. When these hydrates are employed they are usuallypresent as aqueous solutions containing an convenient amount, forexample about 80 to 100 percent by Weight, of the hydrate. The termphosphorus oxide is intended to include the phosphorus oxides set forthabove, and aqueous solutions and hydrates thereof. While aqueoussolutions of phosphoric acid are suitable for use, they tend to causecorrosion when metallic reactors are used. Hence, anhydrous materialsnormally are used in such a case.

The reaction may be conducted simply by mixing benzene with gaseous orliquid chlorine. This process may be performed at various temperatures.When liquid chlorine is used, the temperature usually is below 20 C.,for example, about C. to minus 33 C. Not infrequently, the reaction isperformed by mixing liquid benzene with liquid chlorine at thetemperature at which chlorine remains liquid, and allowing the mixtureto stand under chlorine reflux.

Alternatively, a solution of chlorine in inert solvents, such as carbontetrachloride, or similar solvent, may be placed in a reactor and liquidbenzene may be added from time to time, or continuously, to the chlorinesolution. In this case, the phosphorus compound may be dissolved ordispersed in the liquid chlorine or chlorine solution, or it may bedispersed in the benzene which is added to the chlorine. Moreover thetemperature of reaction may be maintained higher although usually notabove 60 C. b

Although actinic light has been found a very satisfactory means ofactivating the reaction between chlorine and benzene, chemical catalystsmay be adapted to the process to obtain a benzene hexachloride ofsatisfactory gamma isomer content. Such catalysts may supplement or evencompletely replace actinic radiation.

Various peroxydicarbonate esters having the probable structure.

Ro-ooo-ooR t t which may be prepared by reacting sodium peroxide with achloroformate in aqueous media, usually at 0 to C., may be employed inthis manner. These esters may be regarded as esters of the hypotheticalperoxydicarbonic acid having the probable structure:

n-ocoo-o-on H H o 0 They normally are liquids or white solids which aresoluble in organic solvents, such as methyl or ethyl alcohol.

Typical peroxydicarbonates useful for this purpose include theperox'ydicarbonate esters of ethyl alcohol, isopropyl alcohol, n-propylalcohol, cyclohexyl alcohol, ethylene glycol, allyl alcohol,Z-nitropro'pahol, phenol, ethyl lactate, benzyl alcohol, cresol, toluol,ethyl salicylate, and correspending esters of other alcohols orcompounds which contain a hydroxy group which is esterified b acids.Such hydroxy compounds rarely contain over carbon atoms, and generallycontain no more than 10 carbon atoms.

other catalysts include organic peroxides, such as benzoyl peroxide,acetyl peroxide, tertiary butyl peroxide, etc. It has also been foundthat a small amount of water seems to aid in providing 4 satisfactoryresults, especially when phosphoryl chloride and phopshoruspentachloride are employed.

When catalysts are used, they are added periodically or continuously tothe mixture, frequently with the benzene as a benzene solution. Usuallya catalyst concentration of 0.01 to 1 percent of catalyst, based uponthe weight of benzene, is suitable.

In performance of the invention, benzene hexachloride is produced asdescribed above, in the presence or absence of phosphorus compounds. Thecrude benzene hexachloride product is present as a solution in theunreacted benzene and/or as a solid. suspended in the liquid reactionmixture. Also present in the reaction mixture are chlorine, benzene, andvarious chlorinated benzenes. The final benzene hexachloride product maybe obtained from this reaction mixture by heating the reaction mixturein the presence of the phosphorus compound which may be added beforechlorination is initiated or any time thereafter. The heating is carriedout at temperatures suificient to vaporize part or all of the impuritiespresent in the benzene hexachloride product. Usually temperatures aboveC. and up to 200 C. are employed to drive out all the impurities fromthe product, although higher temperatures below decompositiontemperatures are permissible. This heating may be carried out atatmospheric pressure, or at pressures below atmospheric pressure.Following the heating operation, the molten product is cooled tocrystallize solid benzene hexachloride using con- Ventional flaking orcrystallization processes.

The amount of phosphorus compound which is sufiicient to eliminate thetendency of the henzene hexachloride product to discolor duringpurification by heating the crude product or the reaction mixturecontaining the product is quite small. In fact, even traces have beenobserved to eliminate the discoloring. For most purposes, it has beenfound that 0.01 to 0.25 percent of phosphorus compound, based upon theweight of benzene hexachloride produced, is satisfactory.

Excessively large amounts of the phosphorus compounds do not appear tobe desirable since charring of the product tends to occur.

The following examples clearly point out the advantage of the use of aphosphorus compound in the above described procedures. Examples I andIII set forth the results when phosphorus pentoxide is used, andExamples II and IV illustrate the difficulties involved in attempting toobtain a white, non-contaminated product of henzene hexachloride withoutuse of a phosphorus compound of the type contemplated in the inventionand set forth above. Examples V and VI show further embodiments of theinvention.

Ema'mple I A 500-cubic centimeter round-bottom, threenecked flask wasfitted with a Water-cooled condenser, an electrically driven, groundglass, sealed, propeller-type glass stirrer, and an elongated connectionwhich served as a chlorine inlet tube and an entrance for a minus 100 C.to 50 C. thermometer. The apparatus above the liquid level of thereaction was covered with aluminum foil, and the reaction mixture wasirradiated with a MO-watt mercury vapor lamp placed 24 inches from thereaction flask.

Three moles (235 grams) of benzene and 0.16- 0.19 gram of phosphoruspentoxide were added to the reaction flask. Chlorine gas addition wasbegun from a cylinder when the benzene was warmed to 40 C. and the lightreached full intensity. The chlorine was added at a rate of 0.72 gramper minute. The stirred reaction mixture was maintained at 40 C.throughout the chlorine addition by intermittent cooling with an icewater bath. After 91 minutes, when 65.5 grams (0.92 mole) of chlorine,suificient for a 10.5 percent benzene conversion, had been introduced,solids began to appear, and the chlorine addition was discontinued butirradiation was continued for an additional 30 minutes.

The resultant reaction mixture was then heated to 139* C. in two hours,without stirring. A colorless solution Was present throughout theheating except towards the end when, at a temperature of 123 0., a lightyellow color developed and remained thus, up to 139 C. By the time atemperature of 123 C. was reached, almost all of the distillate (98percent) was collected. The final benzene recovery was 95 percent of theexcess used. The residue was allowed to stand overnight and most of itcrystallized to a white solid leaving only a small amount of yellow oil,probably a solution of benzene hexachloride in benzene or chlorinatedbenzenes. The solid was dried in a vacuum desiccator, and the weight ofthe dried benzene hexachloride was 9012 grams. The benzene hexachloridethus produced was white and undiscolored.

Example II zene hexachloride product was dark grey, almost black.

Example III A 500-cubic centimeter round-bottom, threenecked flask wasfitted with a large cold finger condenser, and an electricallycone-driven, sealed, propellor-type glass stirrer. A Dry Ice trap wasattached to the condenser. The entire apparatus was wrapped withaluminum foil, except for a hole of approximately two inches in diameteron the side of the flask. A 400-watt mercury vapor lamp was placed in ahorizontal position 24 inches from the hole in the foil.

Five hundred twenty-five grams (7.44 moles) of liquid chlorine, 0.27gram (0.0019 mole) of powdered phosphorus pentoxide, and 79 grams (1.01moles) of benzene were mixed in the reac'-- tion flask. The total volumeof solution was 425 cubic centimeters. The reactants were exposed to thelamp at full intensity for four hours, and then irradiation wasdiscontinued. The slurry was left overnight to permit escape of gaseouscomponents.

The resultant reaction mixture was heated in an oil bath at 130 C. for3.5 hours with intermittent stirring. The color of the mixture was whiteat the end of the heating. The mixture was allowed to cool, whereupon itcrystallized to a waxy, white solid.

6 Example IV The same apparatus and procedure were employed as inExample III, with the exception that no phosphorus pentoxide was used inthe reaction. The reaction mixture, upon being heated to C. in an oilbath, turned black within 20 minutes and remained black throughout the3.5 hours of heating. The final product was black.

Example V The same apparatus was employed as used in Example I. Two andtwo-tenths moles (172 grams) of benzene were placed in the reactionflask and 1.32 moles (94 grams) of chlorine were slowly added to thebenzene while maintaining the temperature at about 20 C. When about 20percent of the benzene had been converted to benzene hexachloride, andafter chlorination had been discontinued, 0.20 gram of phosphoruspentoxide were added to the reaction mixture and the excess benzene wasdistilled off. The product was then heated to a temperature of about C.The benzene hexachloride thus produced was a white solid.

Example VI Forty gallons of benzene and 100 milliliters of an aqueoussolution of phosphoric acid containing 85 percent by weight ofphosphoric acid were placed in a nickel kettle and stirred at atemperature of 20 C. until thoroughly mixed. The contents of the kettlewere irradiated with a 400-watt mercury vapor lamp. Chlorine was thenadded at a uniform rate during irradiation and over a period of 8 hoursin amount sufficient to convert approximately 28 percent of the benzeneto benzene hexachloride at a temperature of 20 C.

After the addition of the chlorine, the excess benzene was distilledoff, and the product was then heated to 140 C. at a final pressure of 80millimeters. The benzene hexachloride thus produced was a white solid.

Although the present invention has been described with respect to thespecific details of certain embodiments, such details shall not beregarded as limiting the scope of the invention except insofar asincluded in the accompanying claims.

I claim:

1. A method of purifying benzene hexachloride contaminated withimpurities present incident to the production thereof by additivechlorination of benzene with chlorine, which comprises agi tating andheating the benzene hexachloride to vaporize impurities therefrom in thepresence of a small amount of a phosphorus oxide.

2. A method of purifying benzene hexachloride contaminated withimpurities present incident to the production thereof by additivechlorination of benzene with chlorine, which comprises agitating andheating the benzene hexachloride to vaporize impurities therefrom in thepresence of a small amount of phosphoric acid.

3. A method of purifying benzene hexachloride contaminated withimpurities present incident to the production thereof by additivechlorination of benzene with chlorine, which comprises agitating andheating the benzene hexachloride to vaporize impurities therefrom in thepresence of a small amount of phosphoryl chloride.

4. A method of purifying benzene hexachloride contaminated withimpurities present incident to the production thereof by additivechlorination of benzene with chlorine, which comprises agitating andheating the benzene hexachloride to vaporize impurities therefrom in thepresence of a small amount of phosphorus pentachloride.

5. A method of purifying benzene hexachloride contaminated withimpurities incident to the production thereof by additive chlorinationof benzene with chlorine, which comprises agitating and heating benzenehexachloride to vaporize impurities therefrom in the presence of a smallamount of a compound selected from the group consisting of phosphorylchloride, phosphorus pentachloride, phosphorus oxides and hydratesthereof.

6. A method of producing benzene hexachloride which comprises reactingchlorine with an amount of benzene in excess of that theoreticallyrequired to react with chlorine under conditions conducive to theproduction of benzene hexachloride whereby to produce a benzenehexachloride solution, adding a small amount of a compound selected fromthe group consisting of phosphoryl chloride, phosphorus pentachloride,phosphorus oxides and hydrates thereof to the solution, agitating thecompound-containing solution, and heating the agitatedcompoundcontaining solution to a temperature and for a time sul'Ticientto drive 01f substantially all of the excess benzene.

, 7. A method of producing benzene hexachloride which comprises reactingchlorine with an amount of benzene in excess of that required to reactwith chlorine under conditions conducive to the production of benzenehexachloride whereby to produce a benzene hexachloride solution,performing said reaction while agitating the reactants in the presenceof a compound selected from the group consisting of phosphoryl chloride.phosphorus pentachloride, phosphorus oxides and hydrates thereof, andthen heating the solution to a temperature and for a'time sufficient todrive off substantially all of the excess benzene.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,010,841 Bender Aug. 13, 1935 FOREIGN PATENTS Number CountryDate 613,519 Great Britain Nov. 30, 1948 OTHER REFERENCES Groggins, UnitProcesses in Organic Synthesis, third edition, page 168 (1947).

6. A METHOD OF PRODUCING BENZENE HEXACHLORIDE WHICH COMPRISES REACTINGCHLORINE WITH AN AMOUNT OF BENZENE IN EXCESS OF THAT THEORETICALLYREQUIRED TO REACT WITH CHLORINE UNDER CONDITIONS CONDUCTIVE TO THEPRODUCTION OF BENZENE HEXACHLORIDE WHEREBY TO PRODUCE A BENZENEHEXACHLORIDE SOLUTION, ADDING A SMALL AMOUNT OF A COMPOUND SELECTED FROMTHE GROUP CONSISTING OF PHOSPHORYL CHLORIDE, PHOSPHORUS PENTACHLORIDE,PHOSPHORUS OXIDES AND HYDRATES THEREOF TO THE SOLUTION, AGITATING THECOMPOUND-CONTAINING SOLUTION, AND HEATING THE AGITATEDCOMPOUNDCONTAINING SOLUTION TO A TEMPERATURE AND FOR A TIME SUFFICIENTTO DRIVE OFF SUBSTANTIALLY ALL OF THE EXCESS BENZENE.